Optimizing nitrogen input to reduce nitrate leaching loss in greenhouse vegetable production

Overuse or misuse of nitrogen (N) fertilizers in intensive greenhouse vegetable production regions has been recognized as a non-point source pollution to environmental quality. The objectives of this study were to study the potential of N leaching in intensive greenhouse vegetable systems of southern China and to investigate strategies in minimizing the impact of N loss on water quality. A consecutive four-year field experiment was conducted with five N (manure + urea) application rates (234 + 0, 234 + 348, 234 + 522, 234 + 696, and 234 + 870 kg N ha−1 a−1) in a tomato, cucumber, and celery annual rotation system. The results demonstrated that the amount of N leached was 181.6–276.9 kg N ha−1 a−1 under traditional N rates of 1104 kg N ha−1 a−1 used by local farmers; this leaching loss mainly occurred during the open-field (the polyethylene-cover was not in use) periods. The leached water flux and the total N concentration in the leachates determined by a lysimeter were 205.1–288.4 mm a−1 and 36.6–171.1 mg L−1 under the traditional N rate, respectively; the flux produced during the open-field was 40.9–58.9% of that for the whole year. By decreasing traditional N rate of synthetic fertilizer by 40%, N leaching loss was reduced by 39.6% without any yield loss in intensive greenhouse vegetable production systems.